WO2014/029873 describes structure for draining surface water from sports grounds comprising a coherent force distribution layer and a drain layer. The drain layer is formed of an array of coherent man-made vitreous fibre (MMVF) drain elements, each of the drain elements comprising fibres bonded with a cured binder composition. The force distribution layer is present to ensure that drain elements positioned below it are not destroyed or do not move out of position when pressure is applied to the surface of the sports ground. The force distribution layer is preferably 1 to 5 cm thick. The force distribution layer may be a coherent MMVF layer, and examples given have a high compressive strength preferably in the range 30 to 60 kPa. Suitable coherent MMVF layers have preferred density in the range 150 to 200 kg/m3, and are preferably rendered coherent using a hydrophilic binder, optionally additionally including a wetting agent. Over the force distribution layer is an upper layer of grass.
In view of the functions of the drain element and force distribution layer, both must be coherent, that is the fibres must be bound together into a coherent mass. The MMVF layers provide moisture management, to avoid sports grounds becoming water-logged, by providing controlled drainage.
NL1013987 discloses the use of stone wool granulate in layers beneath natural grass for improving stabilisation of the soil of the ground thereby improving the flatness of the playing field, even where the grass is played on excessively. The layer into which the stone wool is introduced additionally comprises sand or top-soil in addition to the stone wool granulates. A granulate is a jagged and angular agglomeration of fibres, and this shape avoids displacement of the granulates relative to one another thereby providing the stabilisation. The granulates have sizes up to around 3 mm. These granulates are applied onto a layer of top-soil around 0.08 m thick applied over a layer of sand also present in a thickness of around 0.08 m. After levelling of the stone wool granulate and optional application of fertiliser, a tilling device is used to mix the top layers, ensuring some but not all of the sand layer is mixed. On top of this is applied organic material which is mixed into the underlying layer. Finally the top layers including all of the sand layer are mixed using a harrow. The mixing sequence is intended to move the various materials in a vertical direction only, but also to leave a high content of stone wool granulate and organic material near the surface, and thereby allow the stabilising effect of the stone wool granulates to be achieved. The nature of the starting wool material is not described in detail, for instance regarding the presence of any binder or wetting agent. The present inventors have established that, when granulates of wool remain in grass-growing layers the extent of availability of moisture to the roots of growing plants appears to be limited.
Other descriptions of incorporating stone wool and glass wool into soil based surfaces have been described. For instance in U.S. Pat. No. 5,683,208 bundles of glass filaments are mixed with sand or pulverulent materials to provide sub layers for tracks or roads or sports terrains having improved stability. The bundles of fibres may be produced in situ at the site of the roadway construction, using an apparatus which chops preformed yarns of the glass fibre and distributes this in sand. The process involves distribution of the cut bundles onto a layer of sand on a conveyor, followed by application of another layer of sand, and appears to minimise working of the bundles with sand, while optimising distribution.
A development of the process described in U.S. Pat. No. 5,683,208 is described in WO9721876, where a premix of fibre bundles and sand is produced having the relatively high concentration of fibre, in the range 6-60% by weight. This premix is then mixed as a master-batch into soils or other base material, thereby diluting the fibres in the final product. The master-batch is produced by mixing sand with water and then introducing and mixing the cut bundles of fibres, in a device of the type used to knead doughs. Alternatively, a plough share mixer is used. The process is said to form a master-batch in which the fibres are distributed in a uniform manner in the sand. Even distribution into soil of the fibres is achieved when the master-batch is diluted by mixing into soil.
WO2012123507 provides a method of modifying a riding surface formed of sand, that is used as a non-grassed surface for training and competition, for indoor and outdoor use. The surface is formed of a mixture of sand with stone wool fibres, for instance fibres having good biosolubility at pH 4.5, generally having a length of at least 2000 microns, at least 3000 microns, and having diameters in the range 3-15 μm, preferably in the range 6-12 μm. The fibres are supplied in the form of a granulate which comprises flocks of entangled fibres. Generally the flocks are substantially free of binder and of wetting agent. Preferably the flocks have a low content of shot (particles of size more than 63 μm which are non-fiberised). The stone fibres are preferably blended in an amount in the range 1-30% by weight, preferably in amounts in the range 3-10% by weight. The surface is usually formed by providing a layer of sand onto the surface, distributing the flocks of MMVF wool, followed by compacting the surface using a roller, then wetting the fibres down, followed by mixing using a power harrow, until a homogeneous mixture of sand and fibres covers the surface.
Slabs of mineral fibre wool bound with hydrophilic binder and further impregnated with wetting agent are used extensively as growth media for food crops, especially salad crops in greenhouses or otherwise under plastic. Such slabs are optimised for management of irrigation and nutrition for the plants, and properties which affect root growth have been studied extensively.
Although synthetic soccer pitches are in use in some parts of the world, it is generally far preferred for soccer pitches to be formed of growing grass. Since the pitches must be used over long seasons, and have heavy use, it is important than grass growing conditions are optimised. For this water management of the soil medium in which the grass grows is critical. It is important that the ground does not become water-logged, since growth of the grass suffers and the mechanical characteristics of the surface also deteriorate. It is also important that moisture be available to roots, to allow grass growth, rather than draining to lower layers of ground before the plant roots. Soccer pitches also should provide a range of desired mechanical characteristics in terms of resisting deformation, resisting penetration, whilst having some elasticity so that the surface springs back after being subjected to disrupting forces. There is also a requirement that the grass resist torsion, in order to avoid joint and soft tissue damage to players on the pitch, and to minimise grass roots or soil being torn out in divots, which may require expensive maintenance and repair.
Soccer pitches for use in cold climates may be restricted in terms of the time available for use where, upon reducing temperatures the soil freezes quickly. It would be desirable that frost damage at atmospheric conditions of lowering temperatures be minimised, by providing soil surfaces with reduced rate of cooling.